Cellulose based sustained release macronutrient composition for fertilizer application

ABSTRACT

A macronutrient sustained release composition for a plant locus having nitrogen containing macronutrient compound adsorbed on the surface of hydroxyapatite phosphate nanoparticles, and a process for preparation thereof. The macronutrient adsorbed hydroxyapatite phosphate nanoparticles are encapsulated within cavities present in wood such that the biodegradation of the wood releases the adsorbed macronutrient compounds in a slow and sustained manner to the soil. Further, the macronutrient particles are encapsulated within the cell cavities of wood and wood is coated with cellulose modified hydroxyapatite phosphate nanoparticles such that the rupture of the nanocoating initiates the nitrogen release followed by the biodegradation of the wood releases the rest of the adsorbed macronutrient compounds in a slow and sustained manner to the soil.

FIELD OF THE INVENTION

The present invention relates to nitrogen containing macronutrientcomposition for slow and sustained release in fertilizer applications.More particularly, the present invention relates to urea derivativesthat are encapsulated within a cellulose structure comprising vascularcanals, intercellular spaces and cells.

BACKGROUND OF THE INVENTION

Nutrient availability in the soil-plant system is dictated by complexinteractions between plant roots, soil microorganisms, chemicalreactions and pathways of losses. The macronutrients required by theplant can be lost by chemical processes such as exchange, fixation,precipitation and hydrolysis, and physical processes such as leaching,runoff and volatilization. Nitrogen, phosphorus and potassium (NPK),which are required in large amounts for plants, are not adequatelyavailable in natural soils to support the sustained growth of plants.Therefore, these macronutrients (NPK) are needed to be appliedexternally through fertilizers. Water soluble conventional fertilizerstypically result in a large amount of macronutrients being lost byleaching and evaporation. There is an increased interest in developingslow release fertilizers that release macronutrients to plants overtime. Advantages of slow release fertilizers are improved efficiency andquality as the fertilizer is released over time thus providingsufficient quantities of macronutrients as required for higher cropyields. In addition, slow release fertilizers result in reducedenvironmental damage from leaching of macronutrients into water andemissions as gasses, compared to conventional water soluble fertilizers.

Macronutrients in fertilizers can be applied to the soil as a solid inthe form of a powder or pellets or as a spray. The uptake ofmacronutrients by the plant needs to be compensated by their externalapplication to the soil periodically. Nitrogen is a key macronutrientsource in agriculture particularly for economic crops such as tea,rubber and coconut. Large amount of fertilizer is applied to the soil ofthe tea plant to improve the quality and the yield of the leavesproduced. For example, a study in Japan (Yamada et al., Journal of Waterand Environmental Technology, 7, 4, 331-340, 2009) reported that of thelarge amount of amount of nitrogen fertilizer applied to tea, only 12%of the nitrogen input was up taken by the plant and the rest wasdischarged to the environment.

Coconut plants require an equatorial climate with high humidity to grow.Coconut plants and trees are grown in different soil types such aslaterite, coastal sandy, alluvial, and also in reclaimed soils of themarshy lowlands. One of the unique features of coconut trees and plantsare that it tolerates salinity and a wide range of pH (from 5.0-8.0). Interms of fertilizer application, the amount of N, P, and K requiredvaries according to the type of coconut plantation. In addition Mg maybecome important in some soils.

Therefore, one of the unsolved problems of fertilizer application is, inrelation to the amounts of nitrogen applied to soil, the low NitrogenUse Efficiency (NUE) by crops. This is because an excessive amount ofnitrogen, up to 70%, is lost in conventional fertilizers due toleaching, emissions, and long-term incorporation by soil microorganisms.As such, supplying N macronutrient is critical in preventing the declineof productivity and profitability due to degradation and aging of teaplants (Kamau et al., Field Crops Research 1, 108, 60-70, 2008).Attempts to increase the NUE have so far met with little success.

US2006/0135365 discloses wood chips containing macronutrient salts forshort term plant growth and release of macronutrients over a period ofone week. U.S. Pat. No. 7,165,358 disclose woodchips as a substrate formacronutrients for plant growth. U.S. Pat. No. 2,714,553 discloseconverting wood lignin to sugar and forming a urea-formaldehydecondensation product for macronutrient delivery. U.S. Pat. No. 6,900,162discloses a composition containing nitrogen particles adhered by abinder degraded by soil moisture to provide for the slow release. U.S.Pat. No. 7,211,275 B2 discloses a sustained release composite of watersoluble materials that are adsorbed onto an inorganic material and isreleased by acidic fluids in medical applications.

Solutions are needed to provide slow and sustained release macronutrientformulations for plant growth applications. Therefore, macronutrientsincorporated into cavities present in wood could be used to provide slowand sustained release of macronutrients for plant growth.

SUMMARY OF THE INVENTION

Accordingly provided herein is a macronutrient delivery system thatcontains nitrogen containing macronutrient compound adsorbed on thesurface of hydroxyapatite phosphate (HAP) nanoparticles. Thesemacronutrient adsorbed HAP nanoparticles are encapsulated within thecavities present in wood. Alternatively, macronutrient particles havebeen encapsulated within the cavities present in wood followed by a thincoating of cellulose modified HAP nanoparticles. In an embodiment,nitrogen containing macronutrient compounds such as urea, thiourea, or amixture thereof are adsorbed onto the surface of HAP nanoparticles andencapsulated within the cavities present in wood. Also disclosed hereinis a process for the encapsulation of macronutrient adsorbed HAPnanoparticles/macronutrients within the cavities present in wood. Theencapsulated macronutrient adsorbed nanoparticles or macronutrientsencapsulated nanoparticle coated compounds prepared by this process whenapplied to aqueous and terrestrialenvironments released themacronutrient in a slow and sustained manner. It is believed thatmacronutrient adsorbed HAP nanoparticles or macronutrient particles thatare included in the cavities of the wood provide for the release of themacronutrient compound in aqueous and terrestrial environments. The soilin aqueous and terrestrial environments provides the medium fortransport of the macronutrients to the roots of the plant. Embodimentplants and trees include and are not limited to any crop that grows in alow pH environment (low pH crop) such as tea, rubber and coconut.

DESCRIPTION OF THE FIGURES

FIG. 1. XRD pattern of synthesized HAP nanoparticles

FIG. 2. SEM images of synthesized HAP nanoparticles

FIG. 3. XRD pattern of the urea adsorbed HAP nanoparticles

FIG. 4. SEM image of urea adsorbed HAP nanoparticles

FIG. 5. Schematic representation of the possible structure of the ureaadsorbed HAP nanoparticles

FIG. 6. Optical microscopic image of stem cross section of G. sepium

FIG. 7. N release kinetics for soil from sandy soil (a) fertilizercomposition based on urea adsorbed HAP nanoparticles encapsulated withincavities of G. sepium (b) Commercial fertilizer

FIG. 8. N release kinetics for soil at an elevation of 1600 feet (a)fertilizer composition based on urea adsorbed HAP nanoparticlesencapsulated within cavities of G. sepium (b) Commercial fertilizer

FIG. 9. N release kinetics for soil at an elevation of 4000 feet (a)fertilizer composition based on urea adsorbed HAP nanoparticlesencapsulated within cavities of G. sepium (b) Commercial fertilizer

DETAILED DESCRIPTION

Nitrogen containing macronutrient composition for slow and sustainedrelease in fertilizer applications are described in detail herein below.Fertilizers contain micro- and macronutrients that are essential forplant growth.

As referred to herein primary macronutrients are nitrogen (N),phosphorous (P), and potassium (K) while calcium (Ca), magnesium (Mg),and sulfur (S) are secondary macronutrients. All six nutrients areimportant for plant growth.

As referred to herein, micronutrients required in small amounts forplant growth are boron (B), chlorine (CI), manganese (Mn), iron (Fe),zinc (Zn), copper (Cu), molybdenum (Mo) and selenium (Se).

As referred to herein sustained release of macronutrient is release in aconstant and continual manner.

As referred to herein the slow release of macronutrient provides theplant with nutrients gradually over an extended period of time. Soilsapplied with slow release fertilizer that contain macronutrients willrequire less applications of such fertilizer and leads to higherefficiency of macronutrient release compared to conventional fastrelease fertilizers.

As referred to herein the encapsulation refers to localization of themacronutrients within cavities in the wood. Encapsulation can includecovalent bonds, electrostatic bonds, Van der Waals bonds and hydrogenbonds.

Adsorption as defined herein refers to any means that forms a complexbetween the walls of the cavities and nitrogen containing macronutrientcompound; and nitrogen containing macronutrient compound and HAPnanoparticles. Adsorption can include covalent bonds, electrostaticbonds, Van der Waals bonds and hydrogen bonds.

Urea is adsorbed on the surface of hydroxy apatite phosphate (HAP)nanoparticles. After these urea adsorbed HAP nanoparticles areencapsulated within the cavities present in a transporter medium bothnitrogen and phosphorus will be released slowly.

If potassium ions are encapsulated separately into cavities of wood thenthey too would be released slowly.

Coating as defined herein refers to a thin layer of cellulose modifiednanoparticles adsorbed onto the wood surface. Adsorption can includecovalent bonds, electrostatic bonds, Van der Waals bonds and hydrogenbonds.

Plants as referred to herein include trees, seedlings and mature trees.

Transporter media as referred to herein include any media withsufficient cavities for the storage and transport of the macronutrientcompound such as clays, layered double hydroxides, wood, orange peels,lemon peels, banana peels, or other lignin or cellulose containingmaterials.

Cavities as referred to herein include vascular canals, intercellularspaces, spaces present in clays and cells. These cavities are commonlyfound in wooded plants and clays. Examples of suitable wooded plantswith cavities are Gliricidia sepium (Jacq.) Kunth ex Walp and coniferousplants such as those belonging to the family Pinaceae. The size of thecavities varies with maturity of the wooded plant. Cavities such asvascular canals, xylem and phloem, vary in size depending on the age ofthe wooded plant. The xylem transports water while the phloem transportsnutrients and when the wooded plants are dried the aqueous nutrientspresent within the xylem and phloem are removed. The size of thevascular canals can range from 1 to 30 micrometer range. Theintercellular spaces that are found can be in the nanoscale (i.e. below100 nm).

Once encapsulated, these cavities will become reservoirs for storage ofmacronutrients.

Macronutrients in encapsulated HAP nanoparticles or macronutrientslocalized in vascular canals can be released early during fertilizationdue to the large volume of the vascular canals. Cells which are smallerin volume than vascular canals but larger than intercellular spaces canrelease the macronutrients at an intermediate stage duringfertilization. Macronutrient in encapsulated HAP nanoparticles localizedwithin smaller volumes of intercellular spaces may release themacronutrient at the final stages during fertilization. It is believed,not bound by any theory, that smaller cavities adsorb the macronutrientefficiently in encapsulated HAP nanoparticles on the surface wallscomprising cellulose, lignin and hemi-cellulose.

Preparation of Macronutrient Adsorbed HAP Nanoparticles

HAP nanoparticles can be chemically synthesized using calcium hydroxidesuspension and phosphoric acid (Mateus et al., Key EngineeringMaterials, 330-332, 243-246, 2007). Adsorption of nitrogen containingmacronutrient compound such as urea can be facilitated by stirring theHAP nanoparticles in a concentrated urea solution. Other nitrogencontaining macronutrient compounds can also be used for adsorption onthe HAP nanoparticles. Such adsorbed nitrogen containing macronutrientcompounds can be encapsulated within cavities present in wood or anothersuitable transport medium as defined herein.

Encapsulation of Macronutrient Adsorbed HAP Nanoparticles

Encapsulation of the nitrogen containing macronutrient compound adsorbedonto the surface of HAP nanoparticles into the cavities present in thewood is described herein below.

First the nitrogen containing macronutrient compound is adsorbed ontothe surface of HAP nanoparticles which were prepared as described above.

Second the G. sepium wood was cut into pieces of approximately 1 inch inlength and they were partially dried under vacuum. Finally,macronutrient compound adsorbed HAP nanoparticles were encapsulated intothe partially dried G. sepium stem by pressurizing (1 bar-15 bar) themacronutrient compound adsorbed HAP nanoparticle dispersion into thecavities of the wood. Alternatively, macronutrient compound adsorbed HAPnanoparticle dispersion can be encapsulated into the cavities of thewood under vacuum (0-100 kPa). The percentage of N in the macronutrientcompound adsorbed HAP nanoparticles encapsulated within the cavities canvary with age of the wooded plant. In an embodiment the nitrogen contentof G. sepium wood ranged between 6-15% by weight.

Encapsulation of the nitrogen containing macronutrient compound into thecavities present in the wood and coating of the wood with cellulosemodified HAP nanoparticles is described herein below.

G. sepium wood was cut into pieces of approximately 1 inch in length andwere partially dried under vacuum. Macronutrient compound containingnitrogen was encapsulated into the partially dried G. sepium stem bypressurizing (1 bar-15 bar) a saturated solution of nitrogen containingmacronutrient into the cavities of the wood. The micronutrientencapsulated wood was then coated by dipping or spraying with cellulosemodified HAP nanoparticles.

The percentage of N in the macronutrient compound adsorbed HAPnanoparticles encapsulated within the cavities can vary with age of thewooded plant. In an embodiment the nitrogen content of G. sepium woodranged between 10-20% by weight.

Release Behavior in Soils

In certain embodiments a uniform release of nitrogen over a period up to3 months is observed. During fertilization of tea plants, the frequencyof application can be attenuated depending on the fertilizer requirementof a given tea plantation. This can be done by starting a second roundof application at a suitable period prior to reaching the end of thefirst application of the macronutrient adsorbed HAP nanocomposite. Inanother embodiment, multiple applications of the HAP nanocomposite aredistributed on acidic soils within three months. In another embodimentsoil found at about 4000 feet in tea plantations, for example fromThalawakelai, Sri Lanka, can be used for slow and sustained release ofthe nitrogen containing macronutrient. In another embodiment soil foundat about 1600 feet in tea plantations, for example from Kandy, SriLanka, can be used for slow and sustained release of the nitrogencontaining macronutrient.

Sandy soils are suitable for coconut growth and in an embodiment theencapsulated macronutrient releasing nitrogen can be used forfertilization. Further, in an embodiment, the encapsulated macronutrientcan be used to fertilize rubber plants and trees.

Organic matter content of soil between 1600 to 4000 feet elevation canrange from 2 to 3%. In general, higher elevations contain more organicmatter compared to lower elevations such as sea level. Such high organicmatter could lead to lowering of pH of the soil. The macronutrientencapsulated wood cavities are superabsorbent bio polymers such ascellulose, hemi-cellulose and lignin. Such superabsorbent bio polymersabsorb moisture in large amounts and initiates microbial degradationwhen in contact with soils. Acidic products are formed due to themicrobial degradation, and encapsulated macronutrients are released.

In an embodiment, low phosphorous release behavior indicates that P maybe released slower than the depletion of nitrogen during the three monthperiod.

This may be the result of HAP nanoparticles being held tightly withinthe cavities compared to the adsorbed urea. In an embodiment K canexhibit slow and sustained release over the three months period.

EXAMPLES Example 1 Preparation of HAP Nanoparticles

HAP nanoparticles were synthesized by drop wise addition of phosphoricacid (250 ml of 0.6 M) into a suspension of calcium hydroxide (19.29g/250 ml). The reaction was carried out under mechanical stirring (1000rpm). The reaction takes place according to the following equation.6H₃PO₄+10Ca(OH)₂→Ca₁₀(PO₄)₆(OH)₂+18H₂O

HAP nanoparticles synthesized as described above were allowed to settleand the supernatant was decanted. This process was repeated three timesusing distilled water to purify the product. The solid obtained wasdried at 100° C. for two hours to provide 25 g of HAP nanoparticleswhich were characterized using XRD, SEM/EDX, AFM and FTIR.

As seen from FIG. 1, the XRD pattern indicated that the synthesized HAPnanoparticles were identical to a commercial sample obtained from SigmaAldrich Chemical Company, USA. No other peaks were observed confirmingthe absence of any other crystalline impurities. As evidenced by EDXspectra, the presence of Ca and P was confirmed. As seen from FIG. 2,SEM images of HAP nanoparticles, exhibited needle like morphology with adiameter less than 30 nm. AFM images corroborated the uniform particlesize. The particle size distribution was also confirmed by the particlesize measurements done using a Malvern, nanoZS, ZEN 3600.

FTIR spectrum further confirmed the presence of HAP nanoparticles andthe peak assignments are given in Table 1 below:

TABLE 1 FTIR peak assignments for HAP nanoparticles Wavenumber/cm⁻¹ Peakassignment 1080-1020 P—O stretching of PO₄ ³⁻ 3600-3580, 633 O—Hstretching 1640 O—H bending of adsorbed water

Example 2 Synthesis of Urea Adsorbed HAP Nanoparticles

HAP nanoparticles synthesized as described in Example 1 were treatedwith 250 ml of 1M urea solution. The solution was stirred mechanicallyat 750 rpm for 12 hours. In another experiment the solution wassubjected to ultrasonic mixing at 30 kHz for 45 minutes. The excessliquid was decanted and the product was washed to remove the excessurea.

The product was characterized using XRD, SEM/EDX and FTIR. As seen inFIG. 3, XRD pattern of the urea adsorbed HAP nanoparticles indicated thepresence of peaks due to HAP, and an extra peak that was attributed tothe adsorbed urea.

FIG. 4 represents the SEM image of urea adsorbed HAP nanoparticles; theparticle size and the morphology of the HAP nanoparticles were notsignificantly changed by surface adsorption of urea.

Table 2 represents FTIR data obtained for urea, HAP nanoparticles andurea adsorbed HAP nanoparticles.

As seen from Table 2, N—H stretching frequency of pure urea appears as adoublet at 3430 cm⁻¹ and 3340 cm⁻¹ and once urea is bonded to HAPnanoparticles it gives rise to a noticeable shift to 3300 cm⁻¹. Thisshift reveals that the NH₂ groups of urea are bonded to OH groups of HAPnanoparticles via H-bonding. This can be confirmed further by the peakbroadening in the corresponding N—H stretching frequencies of urea. Theband at 1590 cm⁻¹ for the N—H bending motion was still present althoughshifted to 1627 cm⁻¹ for urea adsorbed HAP nanoparticles. This indicatesthe presence of free unbound NH₂ groups even after adsorption of ureaonto the HAP nanoparticles. The relatively free NH₂ groups may be heldwithin the encapsulated structure and may be released at the earlystages during fertilization.

TABLE 2 FTIR peak assignment for urea, HAP nanoparticles and ureaadsorbed HAP nanoparticles. Urea adsorbed Wavenumber/ Wavenumber/ HAPWavenumber/ HAP cm⁻¹ Urea cm⁻¹ nanoparticles cm⁻¹ nanoparticles 3430,3340 N—H ~3300  N—H/O—H doublet stretching broad stretching 1680carbonyl 1666 carbonyl stretching stretching 1590 N—H 1627 N—H bending1460 N—C—N 1446 N—C—N stretching stretching 1030 P—O 1030 P—O stretchingof stretching of PO₄ ³ PO₄ ³ 3500, 633 O—H 3300 O—H stretchingstretching broad 3350-3550 adsorbed or 3350-3550 adsorbed or bound waterbound water 1640 O—H bending 1627 O—H bending

The carbonyl stretching frequency of pure urea appears at 1680 cm⁻¹while the corresponding peak for urea adsorbed HAP nanoparticles is at1666 cm⁻¹. There is a clear shift in stretching frequency of thecarbonyl group for urea adsorbed HAP nanoparticles indicating that ureais bonded to HAP nanoparticles through the carbonyl group. This can befurther confirmed by a noticeable peak shift of the N—C—N stretchingfrequency (1460 cm⁻¹) of urea to a lower frequency in urea adsorbed HAPnanoparticles (1446 cm⁻¹).

Urea may be adsorbed on the surface of HAP by several binding modes ofunequal binding strengths. This can give rise to different bindingenvironments when encapsulated within the cavities of wood, giving riseto different patterns of release behavior when contacted with soils.

According to the elemental analysis, the urea adsorbed HAP nanoparticlescontained 14%; C, 5%; H, 33%; N and 6%; P.

Schematic representation (not drawn to scale) of the structure of theurea adsorbedHAP nanoparticles is given in FIG. 5.

Example 3 Encapsulation of Urea Adsorbed HAP Nanoparticles into theCavities G. sepium

First, G. sepium wood was cut into 1-5 cm pieces and vacuum dried at 0.5bar for 1 hr. The vacuum dried G. sepium pieces were soaked in excessamount of a dispersion made from urea adsorbed HAP nanoparticles. Thissystem was subjected to a pressure of 1 kg cm⁻² for 2-24 hrs. Thepressure treated G. sepium pieces were oven dried at 50° C. for 5 hrsand characterized using NPK elemental analysis, SEM and FTIR.

The presence of nitrogen in G. sepium was confirmed by NPK analysis, 6%;N, 1%; P. The NPK analysis of untreated G. sepium was 1.26%; N, 0.29%; Pand 1.79%; K.

As seen from FIG. 6, the optical micrograph of the G. sepium wood showedthe highly porous structure. In FTIR, the characteristic peaks of HAPnanoparticles, phosphate stretching vibrations around 1050 cm⁻¹, waterbending motions 1680 cm⁻¹, and the broad hydroxyl stretching peak arefound in urea adsorbed HAP nanoparticle encapsulated G. sepium woodconfirming the presence of HAP nanoparticles within the cells. Thecharacteristic doublet in the urea stretching frequency around 3500 cm⁻¹appears as one broad single peak suggesting a chemical bondingenvironment of urea within the cells of the G. sepium wood.

Example 4 Encapsulation of Urea into the Cavities G. sepium and Coatingwith HAP Nanoparticles

First, G. sepium wood was cut in to 1-5 cm pieces and vacuum dried at0.5 bar for 1 hr. The vacuum dried G. sepium pieces (300 g) were soakedin a saturated urea solution (450 g of urea in 2 L of water). Thissystem was subjected to a pressure of 1 kg cm⁻² for 2 hrs. The pressuretreated G. sepium pieces were oven dried at 50° C. for 5 hrs andcharacterized using NPK elemental analysis, SEM and FTIR.

Secondly, a surface coating of cellulose modified HAP nanoparticles wasapplied on urea encapsulated G. Sepium wood. HAP nanoparticles preparedas above was mixed with carboxymethyl cellulose (CMC) solution (50 g CMCin 250 ml water) by dipping. Cellulose modified HAP nanoparticle coatedG. Sepium wood was dried at 50° C. for four hours.

The presence of nitrogen in G. sepium was confirmed by N and P analysis,16%; N, 1%; P. The NPK analysis of untreated G. sepium was 1.26%; N,0.29%; P and 1.79%; K.

Example 5 Release Kinetics of Urea Adsorbed HAP NanoparticlesEncapsulated G. sepium Wood and Commercial Fertilizer

Three soil samples (1000 g each of (a) sandy soil found at sea level;(b) soil found at an elevation of 1600 feet in a tea plantation; and (c)soil found at an elevation of 4000 feet in a tea plantation) were eachmixed with 20 g of commercial fertilizer formulation for tea (T 65); theT65 formulation contained urea (N 11%), super phosphate (P 11%) andpotash (K 11%); and was purchased from Hayleys Agro Ltd., Colombo, SriLanka.

These three soil samples containing commercial T65 fertilizer was filledinto three glass columns. Similarly, three equal amounts of ureaadsorbed HAP nanoparticles encapsulated G. sepium wood and urea adsorbedG. Sepium wood coated with cellulose modified HAP nanoparticles havingan NPK content similar as those used in the commercial samples, weretaken separately and filled into three glass columns containing threesoil samples (a), (b) and (c) as described above. Next, 180 ml water wasadded to all six soil columns until they reached the soil watersaturation point, and maintained the water content approximatelyconstant throughout the period of study. Water (100 ml) was added atfive day intervals prior to elution. The eluted solutions (50 ml) werecollected for NPK analysis. NPK analysis was done by Kjeldhal (N),vanadamolybdate (P) and flame photometry (K).

The N release kinetics is shown in FIGS. 7 through 9. As shown in FIGS.7 through 9, on day 55 the macronutrient adsorbed HAP nanoparticlesencapsulated within cavities of the transporter medium are stillreleasing at a slow and sustained manner such that at least 100 ppm ofnitrogen was being released into the soil, whereas the amount ofnitrogen released by the commercial fertilizer at this time is less.

A slow and sustained release of N over a period of 2 months for both theacidic soils at elevations of 1600 feet (pH of 4.7) and 4000 feet (pH of5.2) and sandy soil (pH 7) was observed. Fluctuations in the N releasekinetics are observed in the columns which contained commercialfertilizer. This was attributed a release of a large quantity during thefirst two weeks followed by the release of very low quantities untilabout day 30 and subsequent depletion to negligible amounts (see FIGS. 7to 9). The Nitrogen release conditions at soils at an elevation of 1600feet and 4000 feet and the sandy soil at sea level indicated thesustained release behavior even after 30 days.

The P release amounts were less than optimal levels required for allthree types of soils.

The invention claimed is:
 1. A macronutrient sustained releasecomposition comprising: a. a macronutrient compound adsorbed on thesurface of a hydroxyapatite phosphate nanoparticle; and b. a mediumcontaining cellulose, lignin, or a combination thereof having aplurality of cavities, wherein said nanoparticle is dispersed within thecavities of said medium.
 2. The composition of claim 1 wherein themedium is coated with cellulose modified hydroxyapatite phosphatenanoparticles.
 3. The composition of claim 1 wherein said macronutrientcompound comprises nitrogen.
 4. The composition of 1 wherein saidmacronutrient compound is urea.
 5. The composition of 1 wherein theplant locus is a low pH crop.
 6. The composition of claim 1 wherein themacronutrient compound comprises urea, thiourea or a mixture thereof. 7.The composition of claim 1 wherein the macronutrient adsorbedhydroxyapatite phosphate nanoparticles have an average particle diameterless than 30 nm.
 8. The composition of claim 2 wherein the cellulosemodified hydroxyapatite phosphate nanoparticles have an average particlediameter less than 30 nm.
 9. The composition of claim 1 wherein adsorbedmacronutrient compounds have a release profile wherein at day 55, atleast 100 ppm/20 g (composition) of a nitrogen macronutrient is beingreleased into the soil.
 10. The composition of claim 2 wherein adsorbedmacronutrient compounds have a release profile wherein at day 55, atleast 100 ppm/20 g (composition) of a nitrogen macronutrient is beingreleased into the soil.
 11. The composition of claim 1 wherein saidmacronutrient compound comprises nitrogen, phosphorous, and potassium.12. The composition of claim 1 wherein said macronutrient compoundcomprises nitrogen and phosphorous.
 13. A process for preparing amacronutrient sustained release composition comprising; a. providinghydroxyapatite phosphate nanoparticles and a medium containingcellulose, lignin, or a combination thereof having cavities; b.contacting the hydroxyapatite phosphate nanoparticles with amacronutrient to form macronutrient adsorbed on the surface ofhydroxyapatite phosphate nanoparticles; and c. encapsulating themacronutrient adsorbed on the surface of hydroxyapatite phosphatenanoparticles within the cavities present in medium containingcellulose, lignin, or a combination thereof.
 14. A process for preparinga macronutrient sustained release composition according to claim 13wherein the macronutrient encapsulated medium is coated with cellulosemodified hydroxyapatite phosphate nanoparticles.
 15. A method ofmacronutrient sustained release to a plant locus comprising: a.providing an encapsulate having a macronutrient compound adsorbed on thesurface of hydroxyapatite phosphate nanoparticles, wherein themacronutrient adsorbed hydroxyapatite phosphate nanoparticles areencapsulated within the cavities present in a medium containingcellulose, lignin, or a combination thereof; b. contacting saidencapsulate with a soil; and c. releasing the macronutrient compoundadsorbed on the surface of the hydroxyapatite phosphate nanoparticles ina slow and sustained manner to the soil.
 16. A method of macronutrientsustained release to a plant locus according to claim 15 wherein themedium containing cellulose, lignin, or a combination thereof is coatedwith cellulose modified hydroxyapatite phosphate nanoparticles.
 17. Themethod of claim 15 further comprising repeating steps a and b within aperiod of three months.
 18. The method of claim 16 further comprisingrepeating steps a and b within a period of three months.
 19. The methodof claim 15 wherein the plant locus is a low pH crop.
 20. The method ofclaim 16 wherein the plant locus is a low pH crop.